I think it does a little of both. Mine still tries to use furinture, but not as much.

A post will help. What helps more, if it is a kitten, is having the nails removed, providing the cat lives inside. My cats are 10 years old, have had all nails removed (four paws) but still go through the motion of sharpening those invisible nails. It's called, nature.

A good quality scratching post placed in the right spot can sidetrack your cat's more aggressive, damaging scratching. And it's a good idea to get an upright one and try a horizontal one too as some cats prefer that. I have one cat that loves to scratch on our oriental rug, not up on furniture so the horizontal works good for him.

It does help them stop scratching other things, especially if you reward them for scratching the post while discouraging them from scratching other things. Understand that this is natural behavior for them for two reasons. First, there are glands in their paws that place a scent on the things they scratch. It's a territory marking behavior. Second, they continually shed the sheaths (the outer layer) of their claws. And that is something that they have to do -- otherwise, their claws literally loop back around and can puncture their paw pads. They can't do that without scratching. If you can clip their claws, that can help. However, that's something that you pretty much have to start doing to them as kittens to get them used to it. I know that some people advocate de-clawing them. But it's important to remember that, while we humans may look at the claws as fingernails, they're not. They're actually the last joint on their "fingers." Declawing is comparable to amputating the end joints on every finger of your hands. It's just cruel, although I have run across one instance where I think it was justified. (A feral cat with cancer who was impossible to medicate otherwise.) If you don't want a pet that claws things from time to time, get a fish.